A rat king is when a group of rats become attached to each other by their respective tails; either because they are tangled, or caked in excrement etc. The rats cannot separate from each other and they become a big Rat King

I'm too scared to clean my closet because of that weird rustling noise: what if there's a rat king in there?!

A rat king is when a guy or girl has their hand in every social group in their school. They "rat" their way into every group's inner circle, and as a result has the whole school hanging by their tails. These people are usually known for their impeccable manipulation tactics and stealth.

Josh was was at that super exclusive house party last night on snapchat, and then met up with the hot Catholic girls across the street. He's such a Rat King.